Recent experiments of Hopkins10 appear to demonstrate conclusively that the discrepancies in the results of different observers are due to different degrees of aeration while heating. This hypothesis finds confirmation also in the work of Drummond and Coward (1. c.).

Zilva11 has observed that ultraviolet rays have a destructive effect upon the vitamin A in butter-fat. Butter and cod liver oil exposed for 8 hours to ultraviolet light undergoes a very noticeable change and the A in it becomes inactivated. That the slight elevation of temperature is not responsible for this is seen from the fact that addition of butter kept for 6 hours at 35° at once induces growth. On the other hand, the experimental evidence indicates clearly that the inactiva-tion is due to the ozone formed by the action of the ultraviolet rays upon the oxygen of the air. Zilva suggests that the same effect would probably be brought about in exposing milk to ultraviolet rays, a point which is worthy of consideration inasmuch as this method has been proposed for sterilizing milk.

Animal tissues (the brain, heart and liver of the pig) which had been dried at 90° were found by Osborne and Mendell2 to retain a considerable amount of A, but these materials were fed at a high level so that a small amount of destruction would not necessarily have been detected.

9 Steenbock, Boutwell and Kent, J. Biol. Ghem. 35, 517, 1918. 10 Hopkins, Biochem. J. 14, 724, 1020. 11 Zilva, Bioch. J. 13, 165, 1010; 14, 740, 1020. 12 Osborne and Mendel, J. Biol. Chem. 34, 17, 1018.

Steam-treated palm kernel oil is recommended as a control fat by Stammers.13 By passing steam through this oil for three or four hours at a temperature of 230° to 260° C. the oil is rendered quite free from vitamin A.

Steenbock and Boutwell14 found A as it occurs in a grain, in leaf and stem tissue, in fleshy roots, and in a cucurbitous vegetable like squash, to be comparatively stable at high temperature. Treatment consisting of autoclaving for three hours at 15 pounds pressure (120° C.) does not destroy any of the A in yellow corn, nor does it oause any noticeable destruction of the A in chard, carrots, sweet potatoes, or squash as demonstrated when these vegetables were fed in amounts varying from 5 to 15 per cent of the ration. If some destruction occurred it was not detected, but with the amount fed the investigators believe that it could not have occurred to any considerable degree, otherwise normal growth or long continued growth with reproduction would not have been possible. In the case of alfalfa the data was not decisive, but it appears that the destruction, if any, was too little to induce deficiency in the ration. No deleterious action of the ensiling process on A could be demonstrated in a short-time experiment.14a.

Sure, Barnett and Read15 report that the vitamin A present in the Georgian velvet bean is stable after autoclaving for one hour at 15 pounds pressure.

With regard to the heat stability of the A present in green cabbage leaves, Delf16 reported that heating for a half hour at temperatures from 100 to 120° caused slight though perceptible deterioration. After heating at 130° for two hours, however, a serious amount of destruction had taken place. Delf and Skelton17 estimated that 86 per cent of the A in cabbage was lost when the cabbage was dried at a low temperature and stored for two weeks. Osborne and Mendel18 claim, however, that these experiments lack adequate controls and are not convincing.

13 Stammers, Biochein. J. 15, 489,1021.

14 Steenbock and Boutwell, J. Biol. Chem. 41, 163, 1920.

14a Fat-soluble A is not destroyed, according to Steenbock, Sell and Buell, by treatment in the proportion of 1 gm. of fat to 2 c. c. of 20% alcoholic potash at 37° C. for 4 hours and for 30 minutes at the boiling temperature. (Steenbock, Sell and Buell, J. Biol. Chem. 47, 89, 1921).

15 Sure, Barnett and Read, Proc. Soc. Biol. Chem. J. Biol. Chem. 46, li, 1921.

16 Delf, Bioch. J. 12, 416, 1918.

17 Delf and Skelton, Bioch. J. 12, 448, 1918.

18 Osborne and Mendel, J. Biol. Chem. 41, 657, 1920.

That drying does not necessarily bring about destruction of A is demonstrated by the successful experiments of Osborne and Mendel19 with rats on a diet including only 0.1 g. of tomato which had been dried at 60° as the sole source of A. McCollum20 discounts the effect of heat on this vitamin entirely, asserting that there is not the slightest danger of destroying the growth-promoting substances in fruits and vegetables by the ordinary canning processes. Campbell and Chick have reported,21 however, that canned "green-leaf vegetables " are lacking in A unless the liquor is included in the portion eaten.

Fig. 4. - The resistance of the fat-soluble vitamin to destruction by saponification of the fats in cod liver oil and butter-fat is indicated by the above curves showing the prompt recovery of growth in rats when an ether extract of a solution of the soaps was added to the basal rations.

Courtesy of Prof. H. Steenbock, M. T. Sell, M. V. Buell and Journal of Biological Chemistry (47, 109, 1921).

19 Osborne and Mendel, J. Biol. Chem. 41, 649,1920. 20McCollum, Am. J. Pub. Health, 8, 191, 1918.

As a result of his earlier work, Drummond was of the opinion that the destruction of A at high temperatures could be neither an oxidation nor a hydrolytic process. Later evidence, however, led him to agree with Hopkins22 that this is an oxidation process.23 On the other hand, Steenbock, Sell, Nelson, and Buell24 have recently reported that the extract of A obtained from alfalfa is not destroyed by oxidation with hydrogen peroxide or by reduction with nascent hydrogen.